The conventional combustion process in diesel engines is initiated by the direct injection of fuel into a combustion chamber containing compressed air. The fuel is almost instantaneously ignited upon injection into the highly compressed combustion chamber, and thus produces a diffusion flame or flame front extending along the plumes of the injected fuel. The fuel is directly injected into the combustion chamber by a fuel injector having a nozzle tip extending into the combustion chamber. For example, the nozzle tip may extend slightly into the combustion chamber from a wall of the chamber located opposite a reciprocating piston of the combustion chamber.
More demanding emissions standards have necessitated attempts at reducing smoke and NOx byproducts of the combustion process, while maintaining or improving fuel efficiency. One approach to meeting the difficult emissions standards includes incorporating what has been referred to as a Homogeneous Charge Compression Ignition (HCCI) process into the engine cycle. The HCCI process may be more accurately referred to as a controlled auto-ignition process. Such a process operates by injecting fuel into the combustion chamber prior to the point at which the combustion chamber reaches a pressure sufficient to auto-ignite the fuel. Such a fuel injection timing allows for compression of a diluted mixture of air and fuel until auto-ignition occurs. This controlled auto-ignition process provides a combustion reaction volumetrically within the engine cylinder as the combustion chamber volume is reduced by the piston. This type of combustion avoids localized high temperature regions associated with the flame fronts, and thereby reduces smoke and NOx byproducts of the combustion.
Conventional fuel injectors used for injecting fuel into highly pressurized or relatively lower pressurized combustion chambers include a nozzle tip having a plurality of passages allowing fuel from the injector to be injected into the combustion chamber. The number, size, and orientation of the passages in the nozzle tip affect the production of smoke, production of NOx, and fuel efficiency associated with the combustion.
U.S. Pat. No. 4,919,093 to Hiraki et al. discloses a direct injection type diesel engine having a fuel injector nozzle tip including a plurality of injection holes arranged in two rows concentrically relative to a longitudinal axis of the injector nozzle. The injection holes of the two rows are disclosed as forming a zigzag pattern. Accordingly, as disclosed in the illustrated embodiments, each of the two rows include the same number of injection holes. Further, Hiraki et al. discloses that the distal-most row of holes form an acute angle of 45° or greater with the longitudinal axis of the injector nozzle.
The number, size, and orientations of the holes of the fuel injector nozzle tip of Hiraki et al. provide a narrow range or diffusion of fuel plumes into the combustion chamber. This is evidenced by the fact that the injector holes of the distal-most row of the nozzle tip are orientated to form an arc of 90° between opposing nozzle holes of the row. Accordingly, a majority of the area within the combustion chamber formed by the 90° arc does not directly receive injected fuel. Such a narrow range of diffusion of fuel plumes limits the mixing of the fuel with the air, thus increasing the localized high temperature regions in the combustion chamber and thereby producing unwanted smoke and NOx.
The present invention provides a fuel system for an internal combustion engine that avoids some or all of the aforesaid shortcomings in the prior art.